1. Field of the Invention
The present invention relates to probes for measuring epidural pressure and the elasticity of brain parenchyma, and more particularly to a probe for accurately measuring epidural pressure and the elasticity of brain parenchyma for use in the field of diagnosis of the neurosurgery.
2. Description of the Background Art
When a patient is suspected to be suffering from acute cerebral hypertension due to injury in the head, infarct edema, intracerebral hemorrhage or the like, or a patient has chronic cerebral hypertension such as hydrocephalus, measuring intracranial pressure, that is, cerebral pressure is particularly important to know the patient's condition and to carry out surgical treatment.
As a method of measuring a cerebral pressure, measuring the epidural pressure of the patient using a cerebral pressure measuring apparatus has been proposed. This epidural pressure closely relates to increase/decrease in intradural pressure, wherein the epidural pressure increases with increase in intradural pressure due to tumefaction of brain parenchyma and decreases with decrease therein, for example.
Accordingly, in order to observe the brain condition of the patient which is changing every moment, it is extremely useful to measure not only the epidural pressure but also the elasticity of brain parenchyma itself. Then, as apparatus for measuring the elasticity of brain parenchyma, Japanese Patent Laying-Open No. 5-115444 discloses an apparatus for measuring both epidural pressure and the elasticity of brain parenchyma.
This apparatus for measuring the elasticity of brain parenchyma disclosed in Japanese Patent Laying-Open No. 5-115444, however, has the following problems.
According to this measuring apparatus, a chamber formed of a thin film with a bag-shape is provided at one end of a flexible hollow tube, which chamber is inserted outside a dura through an opening formed in the patient's cranium. Then, the chamber is filled with air by means of a plunger pump or the like, whereby epidural pressure is measured from the pressure applied to the chamber, using a measuring apparatus provided at the other end of the tube. A small amount of air is further introduced into the chamber and thereafter change in epidural pressure is measured based on the pressure applied to the chamber. Then, the former epidural pressure is compared with the latter, thereby measuring the elasticity of brain parenchyma.
However, epidural pressure is measured by introducing air into a single chamber in stages as described above. Therefore, if the second air introduction is carried out with the epidural pressure in the first cerebral pressure measurement still being applied to the chamber, epidural pressure corresponding to the second air introduction cannot be measured with high precision because of temporary reverse air flow from the chamber, poor response of the chamber to the additional air introduction using a plunger pump or the like.